Evaporation of weak acid containing 25% to 68% of H₂SO₄ and its further use for various needs, for example, in the production of mineral fertilizers, or strengthening of the acid from 68% to 94% with concentrated sulfuric acid or oleum and its further reutilization for ilmenite decomposition. This method is unacceptable for acidic wastes with low concentration of H₂SO₄, due to excessively high capital and operating costs.
- Increased production cost (evaporated sulfuric acid is about 4-5 times more expensive than fresh sulfuric acid).
- Impossibility for most manufacturers to evaporate the entire volume of hydrolysis acid due to the disbalance of flows;
and an attempt to solve the problem by evaporating to a higher concentration leads to a significant increase in capital costs and even greater increase in production costs.
- Generation of iron sulfate monohydrate as a waste with high content of free sulfuric acid, which requires disposal.